The present invention relates, in general, to a synchronizing device for a manual transmission, and, more particularly, to a synchronizer element with integrated thrust member or locking member for use in such a synchronizing device.
Current manual transmissions include synchronizing devices to attain a comfortable shift between individual gear ratios. During gearshift, the synchronizing device matches the circumferential speed of a pinion gear to the circumferential speed of the gearshaft and subsequently effects a positive connection between the gearshaft and the pinion gear. Various designs of synchronizing devices are described in the German Technical Book, entitled "Zahnradgetriebe" by Johannes Loomann, 1996, pages 452 ff.
The synchronizer element, which constitutes an important component of a synchronizing device, connects the gearshaft in fixed rotative engagement with a shift sleeve which is axially moveable between the pinion gears for change of the gear ratio. Typically, the fixed rotative engagement is realized by providing the synchronizer element with a hub which has a splined or toothed circumference in mesh with the gearshaft, and a guide member which has external teeth so in mesh with the inwardly splined shift sleeve that the shift sleeve can move in direction of the longitudinal center axis of the gearshaft. In addition, depending on the design, the synchronizer element may also serve as stop and guide element for synchronizer rings and friction rings, with the synchronizer element having end faces formed with oblong throughbores or recesses for guiding bolts or cams of the synchronizer rings or friction rings. The synchronizer element is further provided with pockets which are evenly spaced about the outer circumference and receive locking members such as locking bolts and ball-shaped locking elements, and thrust members. The locking members hold the shift sleeve in the center position when the synchronizing device is in neutral and no gear ratio is operative so that the pinion gears rotate freely on the gearshaft. In this position, the locking elements are biased by a spring for a press fit in a groove of the shift sleeve, or the locking element acts on a thrust member which is received in a lock-in groove of the shift sleeve. The end faces of the synchronizer element oftentimes serve directly or via an intermediate element, e.g. a disk, as cam surface for the neighboring pinion gears.
In manual transmissions, it is common to position the synchronizing device on the gearshaft between two pinion gears so that the synchronizing device can selectively positively connect the one or the other one of the pinion gears, disposed to the left and to the right of the synchronizing device, with the gearshaft. The synchronizing element is of such design that the attached shift sleeve can move to the left or to the right in axial direction and that, for example in a double cone synchronization, the cams of the inner synchronizer ring are guided in form-fitting manner. Normally, the left and the right pinion gears have identical connecting elements so that the synchronizer element has a symmetric configuration.
However, on occasions, slight structural variations exist between the left and right pinion gears, e.g. when combining forward and reverse gears, so that the left and right portions of the synchronizer element exhibit structural variations.
In synchronizing devices of this type, the thrust members received in the pockets of the synchronizing element effect during gearshifting a pre-synchronization, i.e. a movement of the respective synchronizer ring against a friction area of the neighboring clutch member or intermediate ring, for example in a double cone synchronization of the synchronizing device. Depending on the design of the synchronizing device, the thrust member is biased either directly by one or two springs, or by a pre-loaded locking bolt or spherical locking member in a lock-in groove of the shift sleeve. When axially moving the shift sleeve for selection of a gear, the inner contour of its lock-in groove pushes one end of the thrust member against the synchronizer ring so that the synchronizer ring is pressed against the friction area.
The configuration and profile of the teeth, recesses and/or longitudinal grooves of a synchronizing element are dependent on the shape and operation of its connecting elements. For example, the recesses on the end faces of the synchronizer element may be configured as bores or oblong holes which may extend through or formed as blind holes. The circumferentially spaced pockets for the locking members and thrust members may also be configured as blind holes or longitudinal grooves of different design. As a result of the stated demands with respect to design and construction, the synchronizer elements for synchronizing devices are normally very complex and complicated components.
German Pat. No. DE 195 80 558 describes a synchronizer element having internal teeth for engagement in a gearshaft, and external teeth about its outer circumference for supporting a shift sleeve. Guided in the synchronizer element is a thrust member as a structural unit. The thrust member is formed by a sleeve-shaped housing with bottom for mounting therein of a ball-shaped locking member and a compression spring. Provided on the housing of the thrust member are guide tabs for guiding the structural unit in a T-shaped longitudinal groove of the synchronizer element. Manufacture of such a synchronizer element, in particular on a large scale, is very difficult and expensive because the synchronizer element is made through a material-removal process or material-removing finishing work from blanks. Therefore, manufacture of such synchronizer elements frequently compromises between a functionally necessary diversity of the shape and manufacturing costs so that an optimum operation can oftentimes not be realized.
Normally, synchronizer elements are of very compact and enclosed structure. As a consequence, they have a relatively high weight and require significant use of material. In addition, they are very rigid and enclosed. This adversely affects material consumption during production of the synchronizer element, overall weight of the gearbox, transfer of oscillations and impacts, and oil circulation in the synchronizing device.
Assembly of the synchronizing device requires a loose and individual placement of the thrust members, locking bolts, compression springs or the structural unit, into the synchronizer element, whereby these components are normally spaced about the circumference. The assembly of the synchronizer element is thus cumbersome and time-consuming. Moreover, quality problems may arise when, for example, some components have been overlooked and thus forgotten to be installed.